Vehicle occupant detection systems are useful in connection with air bags and other pyrotechnically deployed restraints as a means of judging whether, and how forcefully, to deploy the restraint. One fundamental parameter in this regard is the weight of the occupant, as weight may be used as a criterion to classify the occupant. In particular, vehicle manufacturers want the ability to reliably distinguish between a 5th percentile female occupant, a seated child, and a child or infant seat. Typically, normal energy deployment is enabled for a 5th percentile female, reduced energy deployment is enabled for a seated child, and deployment is disabled for a child seat or infant seat.
Although various ways of estimating occupant classification and weight have been devised, perhaps the most simple and cost-effective way involves installing a fluid-filled bladder in or under the bottom foam cushion of the vehicle seat, and measuring the fluid pressure in the bladder with a pressure sensor. Exemplary systems of this type are disclosed, for example, in the U.S. Pat. Nos. 5,987,370 and 6,246,936 to Murphy et al., and the U.S. Pat. Nos. 6,101,436 and 6,490,936 to Fortune et al., all of which are assigned to Delphi Technologies, Inc., and incorporated herein by reference. As disclosed in the above patents, limited occupant classification can be achieved by designing the bladder to tailor its sensitivity based on pressure distribution data, and by analyzing variation in the measured pressure. However, this procedure entails an extensive calibration effort for each different seat design, and necessarily results in a proliferation of bladder designs. It is also known, as described in the U.S. Pat. No. 6,578,871 to Gray et al., to divide the seat bladder into multiple fluid-filled chambers corresponding to different areas of the seat cushion, and to separately measure the fluid pressure in each chamber. While the multiple chamber approach enables improved occupant classification based on weight distribution, the use of multiple pressure sensors is generally cost prohibitive. Accordingly, what is needed is a more cost-effective and less calibration-intensive way of determining the distribution of pressure due to occupant weight in a fluid-filled seat bladder.